Non-oxidising heating of metal articles or blanks



April 29, 1958 o. BALESTRA 2,832,700

NON-OXIDISING HEATING OF METAL ARTICLES OR BLANKS Filed May 4, 1954 2 Sheets-Sheet 1 FIG. 1

April 29, 1958 o. BALESTRA.

NON-OXIDISING HEATING OF METAL ARTICLES 0R BLANKS 2 Sheets-Sheet 2 Filed May 4, 1954 w fi v u u u u iv v 3% Unite States 7 Patent HEATING F METAL ARTICLES 0R BLANKS NON-OXEEING It is known that hot working of metallic workpieces, and particularly those of steel, is rendered difiicult by the impossibility of pre-heating such workpieces economically to a sufiiciently high temperature without surface oxidation.

Unless oxidation of the workpieces is prevented, frictional resistances during hot working increase; the tools employed therefor undergo excessive wear, and the surfaces of the processed workpieces have a poor finish and are defective.

This invention relates to a method and means by which metal articles or blanks may be heated to the desired high temperatures without surface oxidation in furnaces which are conventionally fired.

The improved method consists in coating the metal articles, e. g. blanks or billets, at least within the range 'of temperatures liable to give rise to oxidation, with a film of protective molten material, preferably glass.

This film extends over the whole surface of the workpieces and prevents direct contact thereof with the surrounding atmosphere, which cannot therefore oxidize the metal surface.

The film preserves the metal against oxidation during the whole pre-heating period and the short period dur ing which the articles are conveyed to the pressing or rolling machinery for hot working. The film further affords protection against decarbonising of the metal articles during pro-heating.

Pre-heating carried out according to my improved method not only avoids oxidation of the surface of metallic articles so treated, but also eliminates any previously formed oxide film on the surface thereof. In fact, when glass is used for forming the protective film, the molten .glass efiects a hot pickling of the metal by absorbing iron oxide therefrom.

According to a further feature of the invention, iron oxide itself may be added to the glass in order to modify its melting properties, and suit it to a wide range of working temperatures. It is thus possible to obtain glasses which are fluid at temperatures below 1000" C.

and other types rich in iron oxide which, though they are fluid at about 1400" C., are not subject to over-heating difiiculties otherwise associated with glass at such temperatures such as foaming and swelling of the bath.

This permits of heating the workpieces up and beyond the last-mentioned temperature without the development of surface oxidation thereon.

According to the invention, the protective film is applied to the workpieces by imparting a relative movement to a furnace having a layer of molten material such as glass therein and to the metal articles or blanks contained in the furnace. This may be achieved by imparting a motion to the furnace or to the articles contained therein or to both.

For practice of the method of the invention, the inserted into and removed from the bath when necessary and immersed into the bath in order to coat them with protective material during the heating period.

According to a preferred embodiment, the furnace is of tubular form and is adapted to rotate or oscillate about its own axis. A number of spaced lugs are arranged within the furnace and are formed at their central region with seats substantially aligned with the furnace axis for the introduction and removal of the workpieces in an axial direction. For insertion and removal of the workpieces, the furnace is so positioned that the lugs occupy the lower portion of the furnace chamber and the bath is located between the lugs; during the preheating operation itself, as a result of an angular displacement imparted to the furnace, the lugs are moved laterally, leaving the workpieces in the bath which of course remain in the lower portion of the furnace.

The invention will now be described in detail with reference to the accompanying drawings, which shows diagrammatically and by way of example some embodiments thereof.

Figure l is a longitudinal section of a furnace according to the invention;

Figures 2 and 3 are cross sectional views'of the furnace in the positions for introduction and removal of the workpieces, and for the heating thereof, respectively;

Figure 4 shows a modification of Figure 1;

Figures 5 and 6 are cross sectional views of the furnace shown in Figure 4- on lines V--V and VI- VI of Figure 4, respectively;

Figure 7 shows a further modification of Figure 1.

Referring to Figures 1 to 3, the furnace l is of cylindrical drum shape having at its ends axial openings 2, 3 for the passage of the heating gases and for the introduction and removal of the workpieces. A burner R is located in front of the opening 2 as a source of heat.

The furnace is carried by rollers 4 through which it is rotatable about its axis.

A number of cross partition lugs 5 having each ap proximately the shape of a circular segment are arranged within the furnace and are formed with a concave seat 6, substantially aligned with the furnace axis for supporting the work-pieces P as they are introduced into and removed from the furnace. The lugs are provided laterally of the seat 6 with gradients 7 having inclinations varying gradually and by sets along the furnace axis.

The lugs are suitably spaced so as to contain between them the bath B of a material adapted to prevent oxidation of the workpieces, for example molten glass.

Upon introduction of the workpieces P onto the seats 6, the furnace is rotated through half a turn in the direction of the arrow P (Fig. 2) until it takes the position shown in Figure 3 with the lugs displaced to one side. As a result of this rotation the workpieces roll off one side of the lugs into the underlying bath B.

The workpieces may be submerged in the bath during the whole heating period, so that they are fully protected against oxidation. Should the workpieces be only partly immersed into the bath, they may nevertheless be protected by causing them to roll in the bath by effect of angular oscillations imparted to the furnace so as to form on said workpieces a protective film of molten glass. On completion of heating the furnace is returned to its initial position and the workpieces are gradually collected by the inclined sides 7 of the lugs and returnedto their central seats 6. As so collected they are coated by a molten glass film which further protects them also during removal and transport of the workpieces to the machine for the hot working step.

In the modification shown in Figures 4 to 6, the comformed thereon by the bath B.

' bustion chamber of the furnace encloses at its ends two the furnace in the position shown in Figures 4 and 5,

with its lugs 5, 5a in their lowest position. The workpieces are inserted onto the central seat 6 of the lug 50 adjacent the opening 3, whereupon the furnace is rotated through about half-a-turn in the direction of the arrow F (Figure 5), so that the workpiece P rolls along the "inclined plane 8 and sinks into the underlying hath. 'Upon further rotation of the furnace, the lugs reach the high position shown in Figure 6. The row of workpieces is then axially displaced in order to bring the first workpiece, i. e. that nearest the opening 2, alongside the lug 5 for discharge from the furnace. The furnace is then further rotated in the same direction through about half a turn,'returning it from its position shown in Figure 6 to its initial position shown in Figure 5, the

first workpiece being collected by the gradient 7 and "brought into the central seat 6 in the outlet lug 5, from which it can be withdrawn and discharged from the furnace, as it is protected by the filmof protective material According to the modification shown in Figure 7, the

furnace comprises one ing 5 only at the discharge opening 2, and is free from lugs at the opposite end, the workpieces being charged by directly introducing them into the bath B through the charging opening 3.

The process according to this invention is particularly advantageous when the workpieces are to be heated to temperatures over 1000 C. It can be employed solely within the range of temperatures at which oxidation takes place, in which case the workpieces are preheated within the lower temperature range in a conventional manner.

Although the examples described above relate to furnaces in which the workpieces are situated in one row only, it is understood that the invention comprehends the use of furnaces of a size suitable to receive a plurality of rows of workpieces side by side.

What I claim is:

1. The method of heating metallic workpieces which comprises partly immersing said workpieces in a molten glass, exposing the surface of said molten glass to high temperatures, and systematically altering the portion of the surface of said workpieces immersed in said molten glass.

2. The method of protecting metallic workpieces from oxidation during heating preparatory to hot working which comprises partly immersing said workpieces in a bath of molten glass of depth less than the height of said workpieces as placed in said bath, exposing the surface of said bath to high temperatures, and successively changing the a portions of the surface of said workpieces immersed in said bath. i

3. The method of heating metallic workpieces of substantially cylindrical shape which comprises partly immersing said workpieces in a bath of molten glass, exposing the surface of said bath to high temperatures, and effecting rotation of said workpieces within said bath.

4. The method of protecting steel billets from'oxidation during heating preparatory to hot working which comprises placing said billets in a bath of molten glass of lesser maximum depth than the diameter of said billets, exposing said bath to a flow of high temperature gases, and effecting rotation of said billets relative to the surface of said bath.

5. The method of heating steel workpieces of substantially cylindrical shape which comprises partly immersing said workpieces in a bath of molten glass, exposing said bath to a flow of high temperature gases, and effecting rotation of said workpieces about their cylindrical axes relative to the surface of said bath, whereby the portion of the surface of said workpieces submerged in said bath is changed with said rotation and the cylindrical surfaces of said workpieces are completely and continuously coated with molten glass.

6. The method of heating a metallic workpiece preparatory to hot working thereof which comprises bringing said workpiece into contact with a bath of molten glass, passing a current of hot gases over said bath, effecting relative motion of said workpiece and bath to coat said workpiece with an adherent layer of molten glass and to renew saidlayer from-said bath, and causing a portion of said coated workpiece to emerge from said bath into said current.

7. The method of heating metallic workpieces preparatory to hot working thereof which comprises bringing said workpieces successively into contact with a path of molten glass, passing a current of hot gases over said bath, eflFecting relative motion of said workpieces and bath to coat said workpieces in contact with said bath with an adherent layer of molten glass and to renew said layer from said bath, causing a portion of said coated workpieces to emerge from said bath into said current of hot gases, translating said workpieces successively through said bath from an entrance to an exit point thereof, removing from said path portions thereof exhausted from contact with said workpieces, and replacing said removed portions with fresh glass.

References Cited in the file of this patent UNITED STATES PATENTS 376,421 Wassell Jan. 10, 1888 862,285 Schmidt Aug. 6, 1907 1,452,635 Berninghaus Apr. 24, 1923 1,916,569 Haller July 4, 1933 1,919,136 Smith July 18, 1933 2,009,165 Cross July 23, 1935 2,135,934 Blaiser Nov. 8, 1938 2,235,825 Cary Mar. 25, 1941 2,628,173 Fair Feb. 10, 1953 

1. THE METHOD OF HEATING METALLIC WORKPIECES WHICH COMPRISE PARTLY IMMERSING SAID WORKPIECE IN A MOLTEN GLASS, EXPOSING THE SURFACE OF SAID MOLTEN GLASS TO HIGH TEMPERATURES, AND SYSTEMATICALLY ALTERING THE PORTION OF 